Effect of High Resistance Phases on Metal-Insulator Transition of La_0.67Ca_0.33MnO₃

The temperature dependence of resistivity ρ of YSZ doping composite of (1-x)La_0.67Ca_0.33MnO₃ + xYSZ and Y₂O₃ doping composite of (1-y)La_0.67Ca_0.33MnO₃ + yY₂O₃ is investigated, respectively, in a temperature range 77-300 K, where the YSZ represents yttria-stabilized zirconia (8 mol%Y₂O₃ + 92 mol% ZrO₂). Experimental results show that the YSZ doping level has important effects on both the metal-insulator (M-I) transition temperatures and zero field resistivity of the composites of (1-x)La_0.67Ca_0.33MnO₃ + xYSZ. However, the Y₂O₃ doping level has little effect on the M-I transition temperatures and the zero field resistivity of (1-y)La_0.67Ca_0.33MnO₃ + yY₂O₃ only increases slightly. The difference between the two types of composites may mainly result from the different distribution of high resistance phases at the grain boundaries and/or surfaces of La_0.67Ca_0.33MnO₃ grains rather than the substitution of La³⁺ ions with Y³⁺ ions.